The present invention relates to an ink supply container comprising an ink chamber wherein the ink supply container is provided with an ink filling opening leading into the ink chamber and an ink outflow opening leading out of the ink chamber, the ink outflow opening being suitable for connection to an inkjet printhead, the ink supply container further being provided with, or at least being connectable to, means for maintaining a negative pressure in the ink chamber. The present invention also relates to an inkjet system comprising an inkjet printhead and an ink supply container.
In an inkjet arrangement, a negative pressure should be present in the ink reservoir or in the ink duct connected to the nozzles of an inkjet printhead in order to prevent undesirable leakage of the ink through the nozzles. This requirement means that replenishing an ink supply container with ink is not an immediately simple matter. Unless a closed throwaway system is used, additional means must be provided for replenishment or else the ink supply container must be provided with a special construction to render replenishment possible.
In arrangements where the inkjet printhead is located above the ink reservoir, a negative pressure can be obtained hydrostatically as known, for example, from U.S. Pat. No. 4,571,599. This patent describes how a negative pressure can be maintained at the nozzles of an inkjet printhead by utilizing a completely shut-off main reservoir connected thereto and situated at a lower level than the inkjet printhead, and in which a negative pressure prevails. An auxiliary reservoir is present in this main reservoir and is in liquid communication therewith and contains an air bubble in which the pressure is equal to the atmospheric pressure. The atmospheric pressure is maintained therein by means of a diaphragm which is air-permeable but liquid-impermeable. A change of the ink level and hence of the pressure in the main reservoir is cancelled by admitting air into the auxiliary reservoir. A disadvantage of an arrangement of this kind is the requirement that the ink reservoir must be situated beneath the inkjet printhead in order to obtain the required hydrostatic pressure drop. Also, the system as described is designed as a throwaway system and the ink cannot be replenished.
In arrangements in which the inkjet printhead is situated at the same level as or a lower level than the inkjet reservoir, other methods must be applied to maintain a negative pressure.
For example, U.S. Pat. No. 4,509,062 describes an inkjet arrangement wherein the inkjet printhead is situated beneath a closed ink reservoir. The reservoir is in liquid communication with the nozzles of the inkjet printhead. In this case the required constant negative pressure is obtained by means of a diaphragm defining the ink reservoir, with an external force being applied to the diaphragm by means of a spring. The description also states that the diaphragm and spring can be combined by making the diaphragm of an elastic material. There is no indication how the reservoir can be replenished with ink.
U.S. Pat. No. 5,039,999 describes how a constant negative pressure is maintained in a closed inkjet reservoir by means of a piston in a cylindrical part of the ink reservoir. In this case the cylinder is in liquid communication with the closed ink reservoir. The volume of the ink reservoir is enlarged by the movement of the piston with a negative pressure being obtained therein. The space between the cylinder and the piston wall is, in this case, hermetically sealed by the ink present therein. The ink reservoir is closed by a special filling opening. Air bubbles are trapped in circular grooves between the piston and the cylinder wall. To fill the reservoir, a refill opening is used which is sealed by means of a plug. Continuous or automatic replenishment is not possible with this arrangement.
European Patent EP 0 444 654 describes an inkjet system with a closed ink reservoir provided with an ink injection opening and an air outlet valve. The required negative pressure is obtained by a sponge-like material present in the ink reservoir. In the operating mode, the ink injection opening forms the ink outlet duct so that an inkjet printhead connected to the ink outlet duct must be removed for any replenishment to take place.
European Patent EP 0 645 244 describes an inkjet arrangement wherein the inkjet printhead is situated beneath or next to an ink reservoir. The ink reservoir is removably connected, via a leak-free coupling, to a liquid transport duct leading to the nozzles of an inkjet printhead. The required negative pressure needed to compensate for the hydrostatic pressure and hence the spontaneous leakage of the ink is obtained by the capillary action of a sponge-like material disposed in the ink reservoir. A filter chamber is provided in this liquid transport duct and has therein an ink-permeable filter of metal gauze. The function of the metal gauze is to retain impurities in the ink. The reservoir is replaced when the ink has been used up.
U.S. Pat. No. 4,791,438 describes an inkjet arrangement wherein a negative pressures is maintained in a main reservoir by means of an extra reservoir connected via a capillary duct to the main reservoir, the negative pressure being maintained by the capillary action of said duct. Ink is fed to the extra reservoir via a supply opening intended for this purpose and sealable by means of a plug. Ink cannot be replenished continuously or automatically with this arrangement.